MD_DataIdentification

Maryland Department of Natural Resources requested the collection of LIDAR data over
Kent, Queen Anne and Caroline Counties, MD. In response, EarthData acquired the data
from March 18 through April 6, 2006. Airborne lidar data was acquired at an altitude
of 5,500'(1676.4 m) above mean terrain with a swath width of 40', which yields an
average post spacing of lidar points of no greater than 6.56 ft (2 m). The project
was designed to achieve a vertical accuracy of the lidar points at 7.09 in (18 cm)
root mean square error (RMSE). The flight design included a total of seventy-seven
flight lines with approximately 2,246 total line miles (3614.59 km). The lidar data
was acquired prior to the emergence of deciduous foliage. This is a bare earth data
set. Light Detection and Ranging (LIDAR) is a method of locating objects on the ground
using aerial-borne equipment. It is similar to RADAR or SONAR in that the two-way
travel time of an energy beam reflected off an object is precisely measured, but this
technology uses laser light instead of radio or sound waves. This technology has proven
very useful in remote sensing of the earth. It can be used for determining elevations
of both the earth's surface and items (natural and man-made) on the surface. Analysis
of LiDAR data is used in detailed modeling of the earth's surface for drainage and
floodplain studies, determining how a new structure will affect views from various
locations, shoreline erosion studies, and other reasons. "First returns" are the first
elevation value that the LiDAR sensor recorded for a given x,y coordinate. Likewise,
"last returns" are the last elevation value that the LiDAR sensor recorded for a given
x,y coordinate. The Bare Earth Mass Points are point elevations that represent the
"bare earth." Features that are above the ground - such as buildings, bridges, tree
tops, etc. - are not included in these data. The Gridded DEM is a model of the surface
of the earth (no above-surface features such as buildings, tree tops, etc) with a
point at every 2 meters representing the average surface elevation of that area. The
LIDAR Intensity Imagery are similar to aerial photography. While not as sharp as traditional
aerial photos, they offer a good visual representation of the surface and various
features.

These data depict the elevations at the time of the survey and are only accurate for
that time. Users should be aware that
temporal changes may have occurred since this data set was collected and some parts
of this data may no longer represent actual surface
conditions. Users should not use this data for critical applications without a full
awareness of its limitations. Any conclusions drawn
from analysis of this information are not the responsibility of NOAA or any of its
partners. These data are NOT to be used for navigational purposes.

Source Contribution: Aerial Lidar Acquisition. Maryland Department of Natural Resources
requested the collection of LIDAR data over Kent, Queen Anne and Caroline Counties,
MD. In response EarthData acquired the data from March 18 through April 6, 2006 using
its aircraft with tail number N62912. LIDAR data was captured using an ALS50 LIDAR
system, including an inertial measuring unit (IMU) and a dual frequency GPS receiver.
An additional GPS receiver was in constant operation over a published control point
set by EarthData at the base of operations airport which is a secondary Airport Control
Station. During the data acquisition, the receivers collected phase data at an epoch
rate of 1 Hz. The use of the Airport base station ensured that all data capture was
performed within 50 miles of a base station. The solutions from Kent, Queen Anne and
Caroline counties were found to be of high integrity and met the accuracy requirements
for the project. These accuracy checks also verified that the data meets the guidelines
outlined in FEMA's Guidelines and Specifications for Flood Hazard Mapping Partners
and Appendix 4B, Airborne Light Detection and Ranging Systems. Airspeed - 140 knots
Laser Pulse Rate - 52700 kHz Field of View - 40 degrees ScanRate - 30 Hz Source Type:
Firewire Drive

1

Report of Survey for Caroline, Kent & Queen Anne's Counties

2006-07-12

Source Contribution: Ground Control. Earthdata International was contracted to provide
LIDAR mapping services in the area of Caroline, Kent, and Queen Anne's Counties, Maryland.
Earthdata subcontracted the ground survey tasks to TerraSurv, Inc. The Global Positioning
System (GPS) was used to establish the control network. The horizontal datum was the
North American Datum of 1983, CORS adjustment (NAD 1983 CORS). The vertical datum
was the North American Vertical Datum of 1988(NAVD 1988). There were a total of 27
stations occupied for this project. There were 19 new LIDAR control stations, 2 temporary
GPS base stations, 3 existing NSRS control stations, 2 CORS stations, and 1 airborne
GPS base station used by the flight crew. The network was observed in a radial configuration.
A base receiver was established on a random point and run throughout the observations
in each area. Due to the large area covered, multiple base locations were used. The
temporary base stations were tied to the CORS and NSRS control stations. Source Type:
Electronic mail system

EarthData has developed a unique method for processing lidar data to identify and
remove elevation points falling on vegetation, buildings, and other aboveground structures.
The algorithms for filtering data were utilized within EarthData's proprietary software
and commercial software written by TerraSolid. This software suite of tools provides
efficient processing for small to large-scale, projects and has been incorporated
into ISO 9001 compliant production work flows. The following is a step-by-step breakdown
of the process: 1. Using the lidar data set provided by EarthData, the technician
performs calibrations on the data set. 2. Using the lidar data set provided by EarthData,
the technician performed a visual inspection of the data to verify that the flight
lines overlap correctly. The technician also verified that there were no voids, and
that the data covered the project limits. The technician then selected a series of
areas from the data set and inspected them where adjacent flight lines overlapped.
These overlapping areas were merged and a process which utilizes 3-D Analyst and EarthData's
proprietary software was run to detect and color code the differences in elevation
values and profiles. The technician reviewed these plots and located the areas that
contained systematic errors or distortions that were introduced by the lidar sensor.
3. Systematic distortions highlighted in step 2 were removed and the data was re-inspected.
Corrections and adjustments can involve the application of angular deflection or compensation
for curvature of the ground surface that can be introduced by crossing from one type
of land cover to another. 4. The lidar data for each flight line was trimmed in batch
for the removal of the overlap areas between flight lines. The data was checked against
a control network to ensure that vertical requirements were maintained. Conversion
to the client-specified datum and projections were then completed. The lidar flight
line data sets were then segmented into adjoining tiles for batch processing and data
management. 5. The initial batch-processing run removed 95% of points falling on vegetation.
The algorithm also removed the points that fell on the edge of hard features such
as structures, elevated roadways and bridges. 6. The operator interactively processed
the data using lidar editing tools. During this final phase the operator generated
a TIN based on a desired thematic layers to evaluate the automated classification
performed in step 5. This allowed the operator to quickly re-classify points from
one layer to another and recreate the TIN surface to see the effects of edits. Geo-referenced
images were toggled on or off to aid the operator in identifying problem areas. The
data was also examined with an automated profiling tool to aid the operator in the
reclassification. 7. The final DEM was written to an LAS 1.0 format and also converted
to ASCII 8. The point cloud data were also delivered in LAS 1.0 format and also converted
to ASCII.

1

2006-11-20T00:00:00

EarthData utilizes a combination of proprietary and COTS processes to generate intensity
images from the lidar data. Intensity images are generated from the full points cloud
(minus noise points) and the pixel width is typically matched to the post spacing
of the lidar data to achieve the best resolution. The following steps are used to
produce the intensity: 1) Lidar point cloud is tiled to the deliverable tile layout.
2) All noise points, spikes, and wells are deleted out of the tiles. 3) An EarthData
proprietary piece of software, EEBN2TIF is then used to process out the intensity
values of the lidar. At this point, the pixel size is selected based on best fit or
to match the client specification if noted in the SOW. 4) The software then generates
TIF and .TFW files for each tile. 5) ArcView is used to review and QC the tiles before
delivery.

1

2008-11-03T00:00:00

The NOAA Coastal Services Center (CSC) received the files in las and ASCII format.
The data were in Maryland State Plane Projection, NAVD88 vertical datum and the vertical
units of measure were meters. CSC performed the following processing to the las data
to make it available within Digital Coast: 1. The data were converted from Maryland
State Plane coordinates to geographic coordinates. 2. The data were converted from
NAVD88 (orthometric) heights to GRS80 (ellipsoid) heights using Geoid 03. 3. The LAS
data were sorted by latitude and the headers were updated.

1

2009-07-23T00:00:00

The NOAA National Geophysical Data Center (NGDC) received lidar data files via ftp
transfer from the NOAA Coastal Services Center. The data are
currently being served via NOAA CSC Digital Coast at http://www.csc.noaa.gov/digitalcoast/.
The data can be used to re-populate the system. The data are archived in LAS
or LAZ format. The LAS format is an industry standard for LiDAR data developed by
the American Society of Photogrammetry and Remote Sensing (ASPRS); LAZ is a loseless
compressed version of LAS developed by Martin Isenburg (http://www.laszip.org/). The
data are exclusively in geographic coordinates (either NAD83 or ITRF94). The data
are referenced vertically to the ellipsoid (either GRS80 or ITRF94), allowing for
the ability to apply the most up to date geoid model when transforming to orthometric
heights.